The present disclosure relates to garments and liners for garments worn for protection from a hazardous environment, and more particularly, to such liners and garments worn by firefighters for protection from extreme heat, moisture and abrasion.
Protective garments are designed to shield a wearer from a variety of environmental hazards, and firefighter garments are representative of such garments. Many conventional firefighting ensembles comprise a turnout coat and pant, each of which includes an outer shell, a moisture barrier located beneath the outer shell, a thermal liner located beneath the moisture barrier, and an innermost face cloth layer often bonded to the thermal liner.
The outer shell typically is constructed of an abrasion-, flame- and heat-resistant material such as a woven aramid material, typically NOMEX or KEVLAR (both are trademarks of E.I. DuPont de Nemours & Co., Inc.) or a polybenzimidazole such a PBI (a trademark of Celanese Corp.) fiber material.
The moisture barrier, such as CROSSTECH® moisture barriers (a trademark of W.L. Gore & Associates, Inc.), typically includes a membrane layer which is moisture vapor permeable but impermeable to liquid moisture. The membrane layer is typically bonded to a substrate of at least one flame- and heat-resistant material, such as an aramid or polybenzimidazole material.
The thermal liner typically comprises one or more layers of insulation material, such as relatively thick layers of aramid fiber batting in the form of needlepunched or spunlaced textiles, which are often quilted to a lightweight aramid-containing fabric substrate or face cloth. The batting of the thermal barrier traps air and possesses sufficient loft to provide the necessary thermal resistance, and the fabric substrate protects the batting of the thermal liner from abrasion from the wearer and provides a sensorially appropriate surface.
The aforementioned components conventionally are arranged within the garment so that the moisture barrier layer is positioned between the thermal liner and the outer shell. This is done, in part, to prevent the insulating material of the thermal liner from absorbing an excessive amount of liquid moisture from the ambient environment, for example from fire hose spray or rain, which undesirably increases the overall weight of the garment, and can reduce the thermal resistance characteristics due to water's high thermal conductivity compared to air, increasing risk of burn injury.
A limitation inherent in such an arrangement is that perspiration from the wearer may be absorbed by the thermal liner which can also cause the adverse consequences described.
It is important to note that moisture may also find its way into the various layers of a garment via diffusion and condensation mechanisms. That is, moisture which may be initially localized to an inner or outer layer can move to other locations in the form of water vapor, and may condense in those locations under the appropriate conditions. This means that simply blocking the physical transport of liquid water may not be sufficient in all cases to ensure the appropriate level of thermal protection is maintained.
Moisture within the layers of the garment can also serve as a source for hazardous convective air movement. In firefighting, a situation known as flashover can occur when there is a near-simultaneous ignition of most of the directly exposed combustible material in an enclosed area, and significant heat exposure will occur, and the ability of a garment to provide protection from burn injury may only be a matter of seconds to a few minutes. Lower levels of heat exposure for longer periods of time are also hazardous.
Upon heating, for example from hazardous radiant exposure from a fire at conditions below flashover levels (subflashover), air and any moisture present within the layers of the garment will heat up. Air when laden with moisture can hold significant and hazardous amounts of heat energy, much more so than dry air. As this moisture-laden air expands and moves through the layers of the garment, it can pose serious risk of burn injury if it moves toward the body of the wearer.
The impact of this moisture within the protective garment layers can be highly unpredictable to a wearer of the garment. That is, a wearer, for example a firefighter, may be unable to foresee how much thermal protection has been compromised by moisture in the garment, and so may not be able to effectively adjust their actions to the new level of risk. Additionally, moisture in the garment can reduce the “alarm-time”, the time between when a wearer may begin to feel pain due to hazardous thermal exposure, and when they may experience a second-degree burn injury. This time between pain and burn (also known as escape time), is the critical time a wearer, for example a firefighter, has to reduce their thermal exposure before being severely burned. In many realistic end-use scenarios for wearers of such protective garments, even small differences such as a few lost seconds in time-to-burn and alarm-time can result in serious injury.
Accordingly, there is a need for a protective garment in which the susceptibility to reduced thermal protection due to moisture is minimized.
Attempts have been made to address some of these disadvantages in such conventional protective garments, particularly firefighting garments, by, for example, incorporating water repellant finishes on and within various layers of the garment. It is well known that these finishes have limited effectiveness and limited durability, particularly in the harsh environments common to firefighters. Other attempts have included the use of inherently non-water-absorbing insulative or barrier materials, such as rubber coatings, neoprene layers or closed-cell foams. However, these materials have the undesirable property of being highly impermeable to moisture vapor diffusion, reducing the ability of the wearer to shed heat by the evaporation of perspiration. This high resistance to evaporative transport can result, for example, in elevated core temperatures of the wearer, potentially causing heat stress, heat stroke, and diminished cognitive function, as well as an increase in retained moisture in the system posing additional risk of thermal injury. Further, many of these approaches are no longer consistent with current industry standards, and so can not be used in many protective apparel applications.